The present invention relates to a mobile antenna for communications purposes, and particularly to such an antenna having improved radiation properties.
Vertical antennas are frequently employed on vehicles for both transmitting and receiving purposes, e.g., as an antenna for "citizens-band" communications equipment. Many forms of transmitting and receiving antennas have been proposed, but they frequently suffer from ineffective radiation patterns, difficulty in loading, or unwieldiness and expense resulting from efforts to increase the antenna's effectiveness. A vertical antenna, mounted above a ground plane of a vehicle, may have an input impedence on the order of 18 ohms, which is less than the usual coaxial cable output from the transmitter-receiver. Such an antenna will have a radiation pattern, primarily in the horizontal direction, but appears to waste considerable radiation in directions not of greatest advantage in groundwave, point-to-point communication.